Didn't Universal do something like this for Potter? I had no interest so didn't pay attention, but I thought I read that.
I'd prefer they do both: reserved FP+, and take-a-number concept for standby.
I want to say they did for Diagon Alley, I don't recall it for Hogsmeade. What I'm talking about though, is the same thing as that. The only difference is that Universal wasn't using Universal Express and Disney will be using FP+.
Are you talking about "take a number" to get in the land or to ride one of the two attractions?
The land. However, it could also be used at the attractions, or any thing that has a standby line. They've attempted it at Soarin' before, for example.
To better clarify, FP+ is a reserved window of time, which can be booked in advance of your visit. A take a number system would require that you be in the park to get a number, so not in advance, and wouldn't be stuck to a certain window of time. Unless a ride breaks down during your window, a FP+ reservation won't get pushed back later in the day, a take a number system could move people forward or backward depending how quickly the physical standby line moves.
It would be more in line with the original FP than FP+. However, your number is a place in line and not a return time, it can move forward or backward depending on operating circumstances.
Historically, you get a pager that lights up when it's time to return, similar to the ones they use at the table service restaurants, but I could see them using the My Disney Experience app instead and just hope people pay attention to any notification, so that they can stretch further into the park. A pager could be possible though, because I believe they did that at Disney Springs with Santa, which is also a large amount of space.
What I'm talking about would not be an easy task at this scale, but they have plenty of time to figure out a good process so that the entire park stays relatively busy.